Coaxial cable

Abstract

[Problem] To provide a coaxial cable having the excellent shielding performance and workability of an outer conductor. [Solution] The problem stated above is solved by this coaxial cable comprising: a central conductor 11; an insulator 12 provided at the outer periphery of the central conductor 11; an outer conductor (13, 14) provided at the outer periphery of the insulator 12; and an outer sheath 15 covering the outer conductor (13, 14). The outer conductor (13, 14) is composed of a spiral shield 13 provided by spirally wrapping a thin metal wire around the outer periphery of the insulator 12 and a metal layer double-sided disposition-type resin tape 14 which is wrapped around the spiral shield 13 and on both surfaces of which a metal layer is disposed.

Description

[Technical Field]

[0001] The present invention relates to a coaxial cable, and more particularly to a coaxial cable that is used for antenna wiring within devices and semiconductor devices compatible with the fifth generation communication standard (5G), and has excellent shielding properties and processability for the outer conductor. [Background technology]

[0002] Coaxial cables are used for transmitting high-frequency signals because they have excellent shielding properties against noise and the like. In particular, coaxial cables used in internal device antenna wiring and semiconductor devices are required to have not only excellent shielding properties but also small diameters and good bending characteristics. In response to these requirements, for example, Patent Document 1 proposes a coaxial cable that satisfies shielding properties, flexibility, a small diameter configuration, bending resistance, and cost efficiency, while also improving terminal workability. This coaxial cable has a structure in which a center conductor, an insulator, an outer conductor with a spirally wound shield structure, and an outer jacket are sequentially layered coaxially.

[0003] In recent years, coaxial cables have been used to transmit high-frequency signals within electronic devices that are becoming increasingly smaller, such as personal computers, smartphones, and tablet devices. In particular, coaxial cables used for internal antenna wiring in devices compatible with the fifth-generation communication standard (5G) and for semiconductor devices require coaxial cables with improved shielding effectiveness, as leakage current is amplified by the internal antenna. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-188782 Summary of the Invention [Problem to be solved by the invention]

[0005] In the course of researching coaxial cables to improve the shielding effect, the inventors produced and investigated the following types of outer conductors: (1) a double structure consisting of a thin-wire horizontally wound shield and, for example, a PET tape with a 6 μm thick copper layer on one side, in that order; (2) a triple structure consisting of a thin-wire horizontally wound shield and, for example, a 6 μm thick PET tape with a 6 μm thick copper layer on one side, in that order; and (3) a double structure consisting of a thin-wire horizontally wound shield and, for example, a 15 μm thick copper foil tape, in that order.

[0006] However, the coaxial cable with the outer conductor (1) above had a thin copper layer and did not have sufficient shielding effect. Furthermore, the coaxial cable with the outer conductor (2) above was wound with two layers of PET tape, each with a 6 μm-thick copper layer on one side, as the outer conductor. The PET tape insulated the inner and outer copper layers, and in order to utilize the total 12 μm copper layer to improve shielding, the outer copper layer also needed to be grounded, making processing more difficult. The coaxial cable with the outer conductor (3) above had the drawback of a hard copper foil tape that was difficult to wind and prone to breaking.

[0007] The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a coaxial cable that can be used for internal antenna wiring of devices and semiconductor devices compatible with the fifth-generation communication standard (5G), and that has excellent shielding properties and processability of the outer conductor. [Means for solving the problem]

[0008] The coaxial cable of the present invention is a coaxial cable comprising a central conductor, an insulator arranged around the outer periphery of the central conductor, an outer conductor arranged around the outer periphery of the insulator, and an outer jacket covering the outer conductor, characterized in that the outer conductor is composed of a horizontally wound shield arranged by winding thin metal wires horizontally around the outer periphery of the insulator, and a double-sided metal layer resin tape wound around the horizontally wound shield and having metal layers arranged on both sides.

[0009] According to this invention, the coaxial cable includes a double-sided metal layer resin tape with metal layers on both sides, and winding the double-sided metal layer resin tape provides electrical conductivity between the metal layers on both sides. This ensures a sufficient amount of metal to enhance shielding, and eliminates the need for additional grounding of the outer metal layer, as is the case when winding resin tapes with metal layers on one side. This provides excellent processability. Furthermore, by providing metal layers on both sides, the thickness of each side can be reduced, avoiding the problems of breakage and winding difficulties associated with copper foil tape. This type of coaxial cable offers excellent shielding properties and can be easily processed for grounding and tape winding, making it ideal for use in antenna wiring within devices and semiconductor devices compatible with the fifth-generation communication standard (5G).

[0010] In the coaxial cable according to the present invention, it is preferable that the thickness of each of the metal layers provided on both sides of the double-sided metal layer-arranged resin tape is 6 μm or more and 12 μm or less. According to this invention, since the thickness of each metal layer is within the above range, the metal layers on both sides that are wound with the double-sided metal layer-arranged resin tape and are electrically connected can ensure a metal amount sufficient to enhance shielding properties. Furthermore, by providing metal layers on both sides, the thickness of each side can be made thin, thereby avoiding the breakage and difficulty of winding that are common with copper foil tape.

[0011] In the coaxial cable according to the present invention, it is preferable that the thickness of the double-sided metal layer resin tape is 8 μm or more and 24 μm or less. Since the thickness of the double-sided metal layer resin tape is within the above range, the present invention can also meet the demand for thinner coaxial cables.

[0012] In the coaxial cable according to the present invention, the metal layer double-sided resin tape and the Constitutes the outer covering It is preferable that a resin tape with a single metal layer disposed on one side is wound horizontally between the resin tape and the tape. According to this invention, the thickness of each metal layer of the resin tape with a double metal layer disposed on the other side is set within a range that does not reduce flexibility, and the total amount of metal layers can be increased, thereby improving shielding properties while maintaining productivity.

[0013] In the coaxial cable according to the present invention, the jacket is preferably composed of a resin tape wound around the outer conductor and an extruded sheath covering the resin tape.

[0014] In the coaxial cable according to the present invention, it is preferable that an adhesive layer is provided on one side of the resin tape, and the resin tape is wound with the adhesive layer facing inward. According to this invention, the adhesive layer of the resin tape fixes the double-sided metal layer resin tape or single-sided metal layer resin tape so that it does not shift, so that the horizontally wound shield does not shift even when stress is applied during wiring of the coaxial cable. As a result, a decrease in shielding effectiveness can be suppressed. [Effects of the Invention]

[0015] According to the present invention, a coaxial cable can be provided that is compatible with the fifth-generation communication standard (5G) and is used in internal antenna wiring and semiconductor devices, and that exhibits excellent shielding properties and processability for the outer conductor. In particular, the cable includes a double-sided metal layer resin tape with metal layers on both sides, and when the double-sided metal layer resin tape is wound, the metal layers on both sides are electrically conductive. This ensures a sufficient amount of metal to enhance shielding, and eliminates the need for additional grounding of the outer metal layer, as is the case when resin tape with a metal layer on one side is wound in an overlapping manner, resulting in excellent processability. Furthermore, by providing metal layers on both sides, the thickness of each side can be reduced, thereby avoiding the breakage and difficulty of winding that are common with copper foil tape. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a perspective view showing an example of a coaxial cable according to the present invention; [Figure 2] (A) is an example of an insulator with a solid structure, and (B) is an example of an insulator with a hollow structure. [Figure 3] FIG. 2 is a cross-sectional view of a double-sided metal layer resin tape. [Figure 4]FIG. 10 is a perspective view showing another example of a coaxial cable according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following describes an embodiment of a coaxial cable according to the present invention with reference to the drawings. The present invention includes inventions based on the same technical concept as the embodiments described below and the embodiments shown in the drawings, and the technical scope of the present invention is not limited to the description of the embodiments and the descriptions in the drawings.

[0018] [Coaxial cable] 1, a coaxial cable 10 according to the present invention is a coaxial cable including a central conductor 11, an insulator 12 provided around the central conductor 11, outer conductors (13, 14) provided around the insulator 12, and an outer jacket 15 covering the outer conductors (13, 14). The outer conductors (13, 14) are characterized by a horizontally wound shield 13 formed by horizontally winding thin metal wires around the insulator 12, and a double-sided metal layer resin tape 14 wound around the horizontally wound shield 13 and having metal layers 14a, 14b arranged on both sides thereof.

[0019] This coaxial cable 10 includes a double-sided metal layer resin tape 14 with metal layers 14a and 14b on both sides, and winding the double-sided metal layer resin tape 14 provides electrical continuity between the metal layers 14a and 14b on both sides. This ensures a sufficient amount of metal to enhance shielding, and eliminates the need to ground the outer metal layer, as is the case when winding resin tapes with a metal layer on one side. This results in excellent processability. Furthermore, by providing the metal layers 14a and 14b on both sides, the thickness of each side can be reduced, thereby avoiding the problems of breakage and winding difficulties associated with copper foil tape.

[0020] Each component will be described in detail below.

[0021] As shown in FIG. 1, the coaxial cable 10 is composed of a central conductor 11, an insulator 12 provided around the central conductor 11, outer conductors (13, 14) provided around the insulator 12, and an outer jacket 15 covering the outer conductors (13, 14).

[0022] <Center conductor> The central conductor 11 is composed of a single wire extending in the longitudinal direction of the coaxial cable 10, or is composed of multiple stranded wires. The wire may be any type of conductive metal, but preferred examples include copper wire, copper alloy wire, aluminum wire, aluminum alloy wire, and copper-aluminum composite wire, as well as conductive metal conductors such as copper wire, copper alloy wire, aluminum wire, aluminum alloy wire, and copper-aluminum composite wire, and those with a plating layer applied to their surfaces. From the viewpoint of high frequency applications, copper wire and copper alloy wire are particularly preferred. Preferred plating layers include solder plating, tin plating, gold plating, silver plating, and nickel plating. The cross-sectional shape of the wire is also not particularly limited, but it may be a circular or nearly circular wire, or a rectangular wire.

[0023] The cross-sectional shape of the central conductor 11 is not particularly limited. It may be circular (including elliptical) or rectangular, but is preferably circular. The outer diameter of the central conductor 11 is desirably as large as possible to reduce electrical resistance (AC resistance, conductor resistance). To reduce the final outer diameter of the coaxial cable 10, the outer diameter may be, for example, within a range of approximately 0.09 to 1 mm. An insulating coating (not shown) may be provided on the surface of the central conductor 11 as needed. The type and thickness of the insulating coating are not particularly limited, but a coating that readily decomposes during soldering is preferred, and a thermosetting polyurethane coating is a preferred example.

[0024] <Insulator> As shown in FIGS. 1 and 2, the insulator 12 is a low-dielectric insulating layer continuously provided around the central conductor 11 in the longitudinal direction. The material of the insulator 12 is not particularly limited and can be selected as desired depending on the required impedance characteristics. However, a low-dielectric-constant fluororesin with a dielectric constant of 2.0 to 2.5, such as PFA (ε2.1), ETFE (ε2.5), or FEP (ε2.1), is preferred, with PFA resin being particularly preferred. The material of the insulator 12 may contain a colorant. The thickness of the insulator 12 is also not particularly limited and can be selected as desired depending on the required impedance characteristics. It is preferable that the thickness be within the range of approximately 0.15 to 1.5 mm. The method for forming the insulator 12 is not particularly limited. Solid, hollow, or foamed structures can all be easily formed by extrusion.

[0025] The insulator 12 may have a solid structure as shown in Fig. 2(A), a hollow structure as shown in Fig. 2(B), or a foamed structure (not shown). The hollow structure has a void 12' inside the structure, and the cross-sectional shape may be such that the void 12' is surrounded by an inner annular portion 12a, an outer annular portion 12b, and a connecting portion 12c. The hollow or foamed structure reduces the material density of the insulator 12, which has the additional effect of making the insulator 12 softer.

[0026] <Outer conductor> As shown in FIG. 1 , the outer conductors (13, 14) are disposed on the outer periphery of the insulator 12. The outer conductors (13, 14) are composed of a horizontally wound shield 13, which is formed by horizontally winding thin metal wires around the outer periphery of the insulator 12, and a double-sided metal layer resin tape 14, which is wound around the horizontally wound shield 13 and has metal layers 14a, 14b disposed on both sides. The outer conductor having such a double structure has a large conductor cross-sectional area and can reduce insertion loss. Furthermore, the inclusion of the horizontally wound shield 13 allows for a smaller diameter than a braided shield. In particular, the present invention includes the double-sided metal layer resin tape 14, which has metal layers 14a, 14b disposed on both sides. Therefore, by winding the double-sided metal layer resin tape 14, the metal layers 14a, 14b on both sides become conductive, ensuring a sufficient amount of metal to enhance shielding properties. Furthermore, since the resin tape 14 with a double-sided metal layer is provided on the horizontally wound shield 13 in such a manner that it is electrically connected (the thin wires and the metal layer are in direct contact), even if stress is applied to the horizontally wound shield 13 and gaps occur between the thin wires, a decrease in the shielding effect can be suppressed.

[0027] 4, the outer conductor may have a triple-layer structure consisting of a horizontally wound shield 13, a resin tape with a double-sided metal layer 14, and a resin tape with a single-sided metal layer 14'. The triple-layer outer conductor (13, 14, 14') can further increase the conductor cross-sectional area, as with the double-layer outer conductor described above, thereby further reducing insertion loss. The resin tape with a single-sided metal layer 14' used here is wound so that the metal layer on one side faces the resin tape with a double-sided metal layer 14. Therefore, the metal layers on the resin tape with a single-sided metal layer 14' and the resin tape with a double-sided metal layer 14 overlap and are electrically connected, ensuring a sufficient amount of metal to enhance shielding.

[0028] (Horizontal winding shield) As shown in Fig. 1, the spirally wound shield 13 is formed by spirally winding thin metal wires on the insulator 12. The spirally wound thin metal wires may be a single layer as shown in Fig. 1 or a multilayer structure not shown, and are not particularly limited, but a single layer is preferable. Compared to a braided structure in which thin wires are crossed to form twists, the spirally wound shield 13 can be thinner while still providing the same degree of effect (sealing effect, etc.), which is advantageous from the perspective of reducing the diameter of the coaxial cable 10.

[0029] The fine metal wires are not particularly limited as long as they are fine metal wires with good conductivity that can be provided around the insulator 12 as the spirally wound shield 13 constituting the coaxial cable 10. For example, various fine metal wires, such as tin-plated copper wire, can be preferably used. The outer diameter of the fine metal wires is not particularly limited and is determined in relation to the outer diameter of the insulator 12, but can be, for example, in the range of about 0.04 to 0.1 mm. The number of fine metal wires is also selected arbitrarily depending on the outer diameter of the insulator 12, the intended outer diameter of the coaxial cable 10, etc. The spiral winding pitch when the fine metal wires are spirally wound is also not particularly limited, but is usually preferably about 0.5 to 11 mm.

[0030] (Double-sided metal layer resin tape) As shown in FIG. 1, the double-sided metal layer resin tape 14 is wound laterally (spiral wound) on the horizontally wound shield 13. As shown in FIG. 3, the double-sided metal layer resin tape 14 is composed of at least a resin substrate 14c and metal layers 14a and 14b provided on the outermost surfaces of both sides of the resin substrate 14c. The terms "at least" and "outermost surface" mean that other layers may be provided between the resin substrate and the metal layer or on the other surface of the resin substrate. The metal layer may be on the horizontally wound shield 13 side on the side indicated by reference numeral 14a, or on the side indicated by reference numeral 14b.

[0031] When the resin tape 14 with double-sided metal layers is wound around the laterally wound shield 13, the metal layers 14a and 14b on both sides are electrically conductive. This ensures a sufficient amount of metal to enhance shielding properties, and eliminates the need for additional grounding of the outer metal layer, as is required when overlapping resin tapes with a metal layer on one side, resulting in excellent processability. Furthermore, by providing the metal layers 14a and 14b on both sides, the thickness of each side can be reduced, thereby avoiding the problems of breakage and winding difficulties associated with copper foil tape. The use of this resin tape with double-sided metal layers 14 allows for the realization of a coaxial cable 10 with excellent shielding properties and easy processability, such as for grounding connections and tape winding.

[0032] The resin substrate 14c is not particularly limited, but a polyester film such as polyethylene terephthalate or polyethylene naphthalate can be preferably used. The thickness of the resin substrate 14c can be selected arbitrarily from readily available materials within a range of, for example, about 2 to 16 μm.

[0033] The metal layers 14a and 14b are preferably copper layers, aluminum layers, etc. The metal layers 14a and 14b are preferably films formed on the resin substrate 14c by vapor deposition or plating, or metal foils bonded to the resin substrate 14c via an adhesive layer (e.g., a polyester-based thermoplastic adhesive resin) provided as needed.

[0034] Because the metal layers 14a, 14b on both sides of the double-sided metal layer-arranged resin tape 14 become conductive when wound, the thickness of the metal layers 14a, 14b is preferably a thickness that ensures a sufficient amount of metal to provide good shielding. The thickness of each of the metal layers 14a, 14b that ensures a sufficient amount of metal is preferably within a range of 6 μm to 12 μm. Within the above thickness range, the metal layers 14a, 14b may be provided on both sides with the same thickness or with different thicknesses. If the thickness of each of the metal layers 14a, 14b is less than 6 μm, the total thickness is less than 12 μm, and the amount of metal is insufficient, resulting in insufficient shielding. If the thickness of each of the metal layers 14a, 14b exceeds 12 μm, resulting in a total thickness exceeding 24 μm, the rigidity of each metal layer increases, making winding difficult. Taking ease of winding into further consideration, it is more preferable that the thickness of each of the metal layers 14a, 14b be in the range of 6 μm or more and 10 μm or less. Note that as the thickness of the metal layers increases, their rigidity increases, reducing ease of winding. However, this ease of winding depends on the outer diameter of the horizontally wound shield 13 to be wound. If the thickness of each of the metal layers 14a, 14b is a maximum of 12 μm, with a total thickness of a maximum of 24 μm, the horizontally wound shield 13 can be wound without reducing ease of winding as long as its outer diameter after winding is approximately 0.7 mm to 2.1 mm, as in the examples described below.

[0035] The overall thickness of the double-sided metal layer resin tape 14 is the sum of the thickness of the resin base material 14c and the metal layers 14a and 14b, and is preferably within the range of approximately 14 to 26 μm in order to contribute to reducing the diameter of the coaxial cable 10.

[0036] The double-sided metal layer resin tape 14 is overlap wound in a range of 1 / 4 to 1 / 2 overlap. By overlapping within this range, direct contact between the metal layers 14a and 14b constituting the double-sided metal layer resin tape 14 and the horizontally wound shield 13 can be ensured, achieving a stable shielding effect. Furthermore, by horizontally winding with this overlap, the metal layer can be directly arranged on the thin metal wire without creating gaps between the metal layers of the double-sided metal layer resin tape 14. If the overlap is less than 1 / 4, the overlap is small, which may cause misalignment during horizontal winding. If the overlap is more than 1 / 2, the overlap thickness of the double-sided metal layer resin tape 14 becomes too thick, which may be disadvantageous in terms of reducing the diameter. The winding pitch of the double-sided metal layer resin tape 14 is not particularly limited as it can be arbitrarily set depending on the width of the double-sided metal layer resin tape 14 and the wrap, but when the width of the double-sided metal layer resin tape 14 is within a range of, for example, about 3 to 6 mm, the winding pitch is preferably within a range of, for example, 1.5 to 10 mm. The horizontal winding direction of the double-sided metal layer resin tape 14 may be the same as or opposite to the horizontal winding direction of the thin metal wire described above, but the opposite direction is preferred.

[0037] Furthermore, even if a gap occurs in the horizontally wound shield 13, the resin tape 14 with a double-sided metal layer, which has metal layers 14a and 14b on both sides, can suppress a decrease in the shielding effect because the thin wires of the horizontally wound shield 13 and the metal layer of the resin tape 14 with a double-sided metal layer are in direct contact with each other.

[0038] (Resin tape with metal layer on one side) As shown in FIG. 4, a single-sided metal layer resin tape 14' may be wound laterally (spiral wound) on top of the double-sided metal layer resin tape 14. The single-sided metal layer resin tape 14' is composed of at least a resin substrate and a metal layer provided on the outermost surface of one side of the resin substrate (not shown). The terms "at least" and "outermost surface" mean that other layers may be optionally provided between the resin substrate and the metal layer or on the other side of the resin substrate. The single-sided metal layer resin tape 14' is wound laterally with the metal layer provided on one side facing the double-sided metal layer resin tape 14.

[0039] The resin substrate and metal layer constituting the single-sided metal layer resin tape 14' are preferably made of the same material and thickness range as the resin substrate and metal layer constituting the double-sided metal layer resin tape 14 described above. A detailed description of these is omitted here. The thickness of the metal layer is not particularly limited, but is preferably within the range of 3 μm to 12 μm, and more preferably within the range of 3 μm to 6 μm, from the viewpoint of ensuring a sufficient metal content throughout the outer conductor. The total thickness of the single-sided metal layer resin tape 14' varies depending on the thickness of the resin substrate, but is preferably within the range of 5 μm to 18 μm. A triple-layered outer conductor including the single-sided metal layer resin tape 14' can further increase the total metal content and improve shielding properties.

[0040] Furthermore, if the thickness of each of the metal layers (14a, 14b) of the double-sided metal layer resin tape 14 is increased to, for example, more than 12 μm in order to increase the amount of metal, the rigidity of each metal layer increases, reducing flexibility, making winding difficult and reducing productivity. To solve this problem, by providing a single-sided metal layer resin tape 14' on the double-sided metal layer resin tape 14, the thickness of each of the metal layers (14a, 14b) of the double-sided metal layer resin tape 14 is kept within the aforementioned range (6 to 12 μm) that does not reduce flexibility, and the total amount of metal layers can be increased, thereby improving shielding performance while maintaining productivity. By providing a single-sided metal layer resin tape 14' on the double-sided metal layer resin tape 14, the total thickness of the metal layers of each tape can be increased while maintaining ease of winding, thereby improving shielding performance. The total thickness is preferably at least 15 μm greater than the sum of the minimum values ​​of the individual metal layers.

[0041] The single-sided metal layer resin tape 14' is preferably wound in the same overlapping range as the double-sided metal layer resin tape 14, and provides the same effects as those described above. The horizontal winding direction of the single-sided metal layer resin tape 14' may be the same as or opposite to the horizontal winding direction of the double-sided metal layer resin tape 14, but the opposite direction is preferred.

[0042] <Outer cover> As shown in FIG. 1, the outer jacket 15 is provided on the outer periphery of the outer conductor (13, 14). Specifically, it is provided on the outer conductor (on the resin tape 14 with a double-sided metal layer in FIG. 1, and on the resin tape 14' with a single-sided metal layer in FIG. 4). The outer jacket 15 is not particularly limited, but examples thereof include a jacket composed of a resin tape 15a wound on the resin tape 14 with a double-sided metal layer in FIG. 1 or the resin tape 14' with a single-sided metal layer in FIG. 4, and an extruded sheath 15b covering the resin tape 15a. The materials of the resin tape 15a and the extruded sheath 15b are not particularly limited as long as they are insulating. The resin tape 15a may be a resin tape having an adhesive layer on one side, and may be spirally wound on the resin tape 14 with a double-sided metal layer in FIG. 1 or the resin tape 14' with a single-sided metal layer in FIG. 4. The extruded sheath 15b may be an insulating sheath formed by extruding a resin.

[0043] (resin tape) The resin tape 15a is wound laterally (spiral wound) on the double-sided metal layer resin tape 14 shown in FIG. 1 or the single-sided metal layer resin tape 14' shown in FIG. 4. The resin tape 15a does not need to have an adhesive layer, but preferably does. The resin tape 15a with an adhesive layer has a resin substrate and an adhesive layer provided on the outermost surface of one side of the resin substrate. The resin tape 15a is wound laterally with the adhesive layer side facing the double-sided metal layer resin tape 14 or the single-sided metal layer resin tape 14'. This adhesive fixes the resin tape 15a to the double-sided metal layer resin tape 14 or the single-sided metal layer resin tape 14'. Therefore, even if stress is applied during wiring, the double-sided metal layer resin tape 14 or the single-sided metal layer resin tape 14' will not shift, thereby suppressing a decrease in shielding properties. The term "outermost surface" means that other layers may be optionally provided between the resin substrate and the adhesive layer or on the other surface of the resin substrate. Also, no adhesive layer is provided on the other surface, and the extruded sheath 15b formed thereon is not bonded. This has the advantage that, for example, when stress is applied during wiring, slippage occurs at the interface between the resin tape 15a and the extruded sheath 15b, making bending flexible.

[0044] Like the double-sided metal layer resin tape 14 and single-sided metal layer resin tape 14', the resin tape 15a is wound with an overlap of 1 / 4 to 1 / 2. By wrapping within this range, the adhesive layer constituting the resin tape 15a can secure the resin tape 15a itself and also adhere to the double-sided metal layer resin tape 14 or single-sided metal layer resin tape 14', thereby securing the double-sided metal layer resin tape 14 or single-sided metal layer resin tape 14'. If the overlap is less than 1 / 4, the overlap is small, which may cause misalignment during horizontal winding. If the overlap exceeds 1 / 2, the overlap thickness of the resin tape 15a becomes too thick, which may be disadvantageous in terms of reducing the diameter. The winding pitch of the resin tape 15a is determined arbitrarily based on the width of the resin tape 15a and the wrap. However, if the width of the resin tape 15a is within a range of, for example, approximately 3 to 6 mm, the winding pitch is preferably within a range of, for example, 1.5 to 10 mm. The horizontal winding direction of the resin tape 15a may be the same as or opposite to the horizontal winding direction of the above-mentioned double-sided metal layer resin tape 14 or single-sided metal layer resin tape 14', but the opposite direction is preferred.

[0045] The resin substrate constituting the resin tape 15a is not particularly limited, but examples thereof include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide (PA), polyimide (PI), polyphenylene sulfide (PPS), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), fluorinated resin copolymer (perfluoroalkoxy fluororesin: PFA), polyether ether ketone (PEEK), etc. In particular, polyester films such as polyethylene terephthalate and polyethylene naphthalate are preferably used. The thickness of the resin substrate is selected arbitrarily from within a range of, for example, about 2 to 6 μm.

[0046] The adhesive layer that optionally constitutes the resin tape 15a is provided on one side of the resin substrate, and examples of the material for the adhesive layer include a urethane adhesive, an epoxy adhesive, an acrylic adhesive, etc. The thickness of the adhesive layer is not particularly limited, but can be about 1 to 3 μm.

[0047] Regarding this resin tape 15a, if the thickness of the resin tape 15a is T2 and the thickness of the resin tape 14 or the resin tape 14' with a double-sided metal layer is T1, the ratio T2 / T1 is preferably in the range of 1 / 6 (=0.167) to 4 / 5 (=0.8), and more preferably in the range of 1 / 4 (=0.25) to 3 / 5 (=0.600). This reduces the step caused by the thickness of the resin tape 15a (to approximately 7 μm or less) compared to when using only the resin tape 14 with a double-sided metal layer or the resin tape 14' with a single-sided metal layer. This reduces the appearance irregularities caused by the air present in the step. As a result, longitudinal changes in the outer diameter are suppressed, allowing the terminals to be processed under the same conditions when connected to a connector.

[0048] Furthermore, the remaining air expands due to heat during subsequent extrusion molding of the extruded sheath 15b, creating unevenness and deteriorating the appearance. Therefore, extrusion molding is performed while using a vacuum pump to minimize remaining air, but this has not been fully resolved. Such unevenness in appearance changes the outer diameter of the coaxial cable in the longitudinal direction. If the same termination conditions are used when connecting the terminal to a connector, the processing yield deteriorates, requiring the termination conditions to be changed each time. To address this issue, a coaxial cable 10 with a T2 / T1 ratio within the above range can suppress unevenness in appearance and longitudinal change in outer diameter, allowing termination to be performed under the same conditions when connecting the terminal to a connector. Furthermore, the coaxial cable 10 can be made thinner than a braided shield alone, and even if gaps occur in the cross-wrapped shield, the shielding effectiveness can be suppressed from decreasing. As a result, the cable can be made thinner, enabling wiring within a narrow space, making it particularly suitable for use in antenna wiring within devices and semiconductor devices compatible with the fifth-generation communication standard (5G).

[0049] When T2 / T1 is preferably greater than 4 / 5, more preferably greater than 3 / 5, the resin tape 15a may still have a step, resulting in insufficient improvement. When T2 / T1 is preferably less than 1 / 6, more preferably less than 1 / 4, the resin tape 15a may be too thin, resulting in the level of stepping of the double-sided metal layer resin tape 14 or the single-sided metal layer resin tape 14' remaining as is, resulting in insufficient improvement. The size of the step that affects the appearance varies depending on the overall outer diameter. For example, if a step of 10 μm or more occurs, the appearance becomes noticeably uneven. Therefore, it is preferable to limit the step to less than 10 μm. The thickness T2 of the resin tape 15a preferably satisfies the relationship "T2 / T1 = 1 / 6 to 4 / 5," more preferably "T2 / T1 = 1 / 4 to 3 / 5," and is preferably 4 μm or more but less than 10 μm, more specifically, 4 μm or more but less than 9 μm.

[0050] (extruded sheath) The extruded sheath 15b is provided on the resin tape 15a by extrusion molding. Various resins that are used in resin extrusion for jackets can be used as the constituent resin of the extruded sheath 15b. For example, it may be a fluororesin such as PFA, ETFE, or FEP, a vinyl chloride resin, a polyolefin resin such as polyethylene, or a polyester resin such as polyethylene terephthalate. In the coaxial cable 10 according to the present invention, a fluororesin is preferred.

[0051] When providing extrusion sheath 15b, it is preferable to perform extrusion molding while suctioning with a vacuum pump so as to minimize the amount of air remaining between extrusion sheath 15b and resin tape 15a. The total thickness of outer jacket 15 formed by extrusion sheath 15b and resin tape 15a can be set within the range of, for example, approximately 0.1 to 1.0 mm.

[0052] The final outer diameter of the obtained coaxial cable 10 is preferably within the range of about 0.6 to 3.5 mm. [Example]

[0053] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0054] [Example 1] First, a coaxial cable 10 having the configuration shown in FIG. 1 was fabricated. A silver-plated annealed copper wire with an outer diameter of 0.203 mm was used as the central conductor 11. Next, a 0.210 mm-thick PFA resin (manufactured by DuPont, dielectric constant 2.1) was extruded around the central conductor 11 to form the solid structure shown in FIG. 2(A), resulting in an outer diameter of 0.623 mm. Next, a horizontally wound shield 13 and a double-sided metal layer resin tape 14 were provided as the outer conductor. The horizontally wound shield 13 was formed as a single layer on the insulator 12. Specifically, 38 silver-plated annealed copper wires with an outer diameter of 0.050 mm were wound counterclockwise at a pitch of 6.5 mm. The outer diameter after formation was 0.723 mm. Next, the double-sided metal layer resin tape 14 was wound around the horizontally wound shield 13. The double-sided metal layer resin tape 14 used had a total thickness of 14.5 μm and a width of 3 mm, and was made of a 2.5 μm thick PET substrate with 6 μm thick copper foil provided on both sides. This double-sided metal layer resin tape 14 was wrapped around the horizontally wound shield 13 in a 1 / 3 lap (overlapping by 1 mm) in the opposite direction to the winding direction of the horizontally wound shield 13.

[0055] Next, a resin tape 15a having a total thickness of 4 μm and a width of 3 mm, with a 1 μm-thick adhesive layer on one side, was wound onto the double-sided metal layer resin tape 14, with the adhesive layer side facing inward (the side of the double-sided metal layer resin tape 14). The winding configuration was a 1 / 3 overlap (overlapped by 1 mm) in the opposite direction to the winding direction of the double-sided metal layer resin tape 14. Heat was applied during the winding process to bond the adhesive layer to the double-sided metal layer resin tape 14. Subsequently, a PFA resin (manufactured by DuPont) layer was extruded to a thickness of 50 μm while being suctioned with a vacuum pump to produce a coaxial cable 10 with an outer diameter of 0.879 mm as the extruded sheath 15b. In this coaxial cable 10, the thickness T2 of the resin tape 15a and the thickness T1 of the double-sided metal layer resin tape 14 were expressed as T2 / T1=4 / 14.5=0.276.

[0056] [Example 2] In Example 1, the double-sided metal layer resin tape 14 used was a 2.5 μm thick PET substrate with 10 μm thick copper foil provided on both sides, resulting in a total thickness of 22.5 μm and a width of 3 mm. Other than that, a coaxial cable 10 was produced that was the same as in Example 1 and had an outer diameter of 0.903 mm. In this coaxial cable 10, the thickness T2 of the resin tape 15a and the thickness T1 of the double-sided metal layer resin tape 14 were expressed as T2 / T1=4 / 22.5 =0.178.

[0057] [Example 3] In Example 1, a resin tape 15a having a total thickness of 8 μm and a width of 3 mm, with a 1 μm thick adhesive layer provided on one side, was used as the resin tape 15a. Other than that, a coaxial cable 10 having an outer diameter of 0.891 mm was produced in the same manner as in Example 1. In this coaxial cable 10, the thickness T2 of the resin tape 15a and the thickness T1 of the double-sided metal layer-arranged resin tape 14 were such that T2 / T1=8 / 14.5=0.552.

[0058] [Example 4] In Example 1, the double-sided metal layer resin tape 14 used was a 2.5 μm-thick PET substrate with a 6 μm-thick copper foil on one side and a 10 μm-thick copper foil on the other side, resulting in a total thickness of 18.5 μm and a width of 3 mm. This double-sided metal layer resin tape 14 was wrapped in the same wrapping as in Example 1 in the opposite direction to the winding direction of the horizontally wound shield 13, with the 6 μm-thick metal layer facing the horizontally wound shield 13. Otherwise, a coaxial cable 10 having an outer diameter of 0.903 mm was produced in the same manner as in Example 1.

[0059] [Example 5] In Example 1, a single-sided metal layer resin tape 14' was wound horizontally between the double-sided metal layer resin tape 14 and the resin tape 15a. The single-sided metal layer resin tape 14' had a total thickness of 16 μm and a width of 3 mm, with a 12 μm thick copper foil on one side of a 4 μm thick PET substrate. This single-sided metal layer resin tape 14' was wound around the double-sided metal layer resin tape 14 in a 1 / 3 overlap (overlapping by 1 mm) in the opposite direction to the winding direction of the double-sided metal layer resin tape 14, with the metal layer facing the double-sided metal layer resin tape 14. The resin tape 15a was wound around the single-sided metal layer resin tape 14' in the opposite direction to the winding direction of the single-sided metal layer resin tape 14'. The resin tape 15a had a total thickness of 9 μm and a width of 3 mm, with a 1 μm thick adhesive layer on one side. Other than that, the same as in Example 1, and a coaxial cable 10 having an outer diameter of 0.930 mm was produced.

[0060] [Reference example 1] In Example 1, instead of double-sided metal layer resin tape 14, a single-sided metal layer resin tape having a total thickness of 10.5 μm and a width of 3 mm, in which 8 μm thick copper foil was provided on one side of a 2.5 μm thick PET substrate, was used, and wound so that the copper foil faced the horizontally wound shield 13. Other than that, the same as in Example 1, and a coaxial cable 10 having an outer diameter of 0.867 mm was produced.

[0061] [Reference example 2] In Example 1, instead of the double-sided metal layer resin tape 14, a single-sided metal layer resin tape with a total thickness of 13 μm and a width of 3 mm was used, which had a 2.5 μm thick PET substrate with a 10.5 μm thick copper foil on one side, and was wound so that the copper foil was facing the horizontally wound shield 13. Then, the same single-sided metal layer resin tape as above was wound on top of the already wound single-sided metal layer resin tape, with the metal layer facing the same direction but in the opposite winding direction. Otherwise, a coaxial cable 10 with an outer diameter of 0.874 mm was produced in the same manner as in Example 1.

[0062] [Reference example 3] In Example 1, instead of double-sided metal layer resin tape 14, a copper foil tape having a thickness of 15 μm and a width of 3 mm was used and wound around horizontally wound shield 13. Other than that, the same as in Example 1, a coaxial cable 10 having an outer diameter of 0.904 mm was produced.

[0063] [evaluation] The shielding performance was evaluated by measuring the shielding effectiveness using a method conforming to MIL-C-85485A. The shielding performance was judged to be good or bad by this measurement method, with an evaluation result of 70 dB or more being rated as "good shielding performance" and an evaluation result of less than 70 dB being rated as "insufficient shielding performance." The coaxial cables of Examples 1 to 5 had shielding effectiveness of 72.4, 77.2, 73.8, 76.5, and 75.4, respectively, indicating good shielding performance. On the other hand, the coaxial cables of Reference Examples 1 to 3 had shielding effectiveness of 62.2, 60.5, and 68.5, respectively, indicating insufficient shielding performance.

[0064] The reason for the favorable evaluation results of Examples 1 to 5 is that by winding the double-sided metal layer resin tape 14 or the double-sided metal layer resin tape 14 and the single-sided metal layer resin tape 14', the metal layers 14a and 14b on both sides become conductive, ensuring a sufficient amount of metal (total thickness in the range of 12 to 24 μm) to enhance shielding. In Example 5, the thicknesses of the metal layers (14a and 14b) of the double-sided metal layer resin tape 14 are within a thickness range (6 to 12 μm) that does not reduce flexibility, and the single-sided metal layer resin tape 14' with a 12 μm-thick copper foil is further wound. This allows the total amount of metal layers to be increased without impairing the flexibility required for tape winding, thereby improving shielding while maintaining productivity. The reason for the unsatisfactory evaluation results of Reference Example 1 is that although a single-sided metal layer resin tape is wound, the thickness of one side is only 8 μm, which does not ensure a sufficient amount of metal to enhance shielding. The reason for the insufficient evaluation results for Reference Example 2 is that although the resin tape with a single metal layer disposed on one side was wound twice, the metal layers constituting each single metal layer disposed on one side were not conductive, so the thickness on one side was only 10.5 μm, which did not ensure a sufficient amount of metal to improve shielding. Reference Example 3 used a copper foil tape with a thickness of 15 μm, which provided good shielding, but its thickness exceeded 12 μm, making tape winding difficult and prone to cracking and breakage.

[0065] Processability was evaluated based on the ease of grounding from the outer conductor. The coaxial cables of Examples 1 to 5 have a resin tape 14 with a double-sided metal layer wound around the horizontally wound shield 13, with the metal layers 14a and 14b on both sides electrically connected, providing electrical continuity between the horizontally wound shield 13 and the metal layers 14a and 14b. Therefore, unlike Reference Example 2, in which a resin tape with a metal layer on one side is wound in an overlapping manner, there is no need to ground the outer metal layer; grounding can be performed in a single location, making them easy to process. On the other hand, the coaxial cable of Reference Example 2 has a resin tape with a metal layer on one side wound in an overlapping manner, which requires grounding the outer metal layer, making processing difficult. Reference Example 1 has a resin tape with a single-sided metal layer wound around the horizontally wound shield 13, and Reference Example 3 has a copper foil tape wound around the horizontally wound shield 13. In both cases, grounding can be performed in a single location, making processing easy.

[0066] The step and appearance were evaluated visually. The step was less than 10 μm in all of Examples 1 to 5. Extrusion sheath 15b The final appearance of the coaxial cable after providing the gap was slightly variable in Examples 1 to 5, but the terminal processing was also possible under the same conditions. In this way, it was visually confirmed that by reducing the gap, the air layer was reduced, the appearance was improved, and the waviness in the longitudinal direction (variation in outer diameter) was reduced. [Explanation of symbols]

[0067] 10 Coaxial Cable 11 Center conductor 12 Insulators 12a Inner ring 12b Outer ring 12c connection part 12' void 13 Horizontally wound shield 14. Double-sided metal layer resin tape 14' Resin tape with metal layer on one side 14a,14b Metal layer 14c resin base material 15 Envelope 15a resin tape 15b Extruded sheath

Claims

1. A coaxial cable comprising a central conductor, an insulator arranged around the central conductor, an outer conductor arranged around the insulator, and an outer jacket covering the outer conductor, wherein the outer conductor is composed of a horizontally wound shield formed by wrapping thin metal wires horizontally around the outer periphery of the insulator, and a double-sided metal layer resin tape with metal layers arranged on both sides wound around the horizontally wound shield, and a single-sided metal layer resin tape is wound horizontally between the double-sided metal layer resin tape and the resin tape constituting the outer jacket.

2. 2. The coaxial cable according to claim 1, wherein the thickness of each of the metal layers provided on both sides of the double-sided metal layer resin tape is 6 μm or more and 12 μm or less.

3. 2. The coaxial cable according to claim 1, wherein the thickness of the resin tape with a double-sided metal layer is 8 μm or more and 24 μm or less.

4. 4. The coaxial cable according to claim 1, wherein the outer jacket is composed of a resin tape wound around the outer conductor and an extruded sheath covering the resin tape.

5. 5. The coaxial cable according to claim 4, wherein an adhesive layer is provided on one surface of the resin tape, and the resin tape is wound so that the adhesive layer faces inward.

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